As industrial society has developed toward an advanced information age, the importance of electronic displays as a medium for displaying and transferring various pieces of information is increasing day by day. Conventionally, a CRT (Cathode Ray Tube), which is bulky, was widely used therefor, but faces considerable limitations in terms of the space required to mount it, thus making it difficult to manufacture CRTs having larger sizes. Accordingly, CRTs are being replaced with various types of flat panel displays, including liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), and organic electroluminescent displays. Among such flat panel displays, in particular, LCDs, a technologically intensive product resulting from a combination of liquid crystal-semiconductor techniques, are advantageous because they are thin and light and consume little power. Therefore, research and development into structures and manufacturing techniques thereof is continuing. Nowadays, LCDs, which have already been applied in fields such as notebook computers, monitors for desktop computers, and portable personal communication devices (PDAs and mobile phones), are being manufactured in larger sizes, and thus, it is possible to apply LCDs to large-sized TVs, such as HD (High-Definition) TVs. Thereby, LCDs are receiving attention as novel displays able to substitute for CRTs, which used to be synonymous for displays.
In the LCDs, because the liquid crystals themselves cannot emit light, an additional light source is provided at the back surface thereof so that the intensity of light passing through the liquid crystals in each pixel is controlled to realize contrast. More specifically, the LCD, serving as a device for adjusting light transmittance using the electrical properties of liquid crystal material, emits light from a light source lamp mounted to the back surface thereof, and the light thus emitted is passed through various functional prism films or sheets to thus cause light to be uniform and directional, after which such controlled light is also passed through a color filter, thereby realizing red, green, and blue (R, G, B) colors. Furthermore, the LCD is of an indirect light emission type, which realizes an image by controlling the contrast of each pixel through an electrical method. As such, a light-emitting device provided with a light source is regarded as important in determining the quality of the image of the LCD, including brightness and uniformity.
Such a light-emitting device is mainly exemplified by a backlight unit. A general backlight unit is illustrated in FIG. 1. Typically, a backlight unit causes light to be emitted using a light source 1 such as a cold cathode fluorescent lamp (CCFL), so that such emitted light is sequentially passed through a light guide plate 3, a diffusion sheet 4, and a prism sheet 5, thus reaching a liquid crystal panel 6. The light guide plate 3 functions to transfer light emitted from the light source in order to distribute it over the entire front surface of the liquid crystal panel 6, which is planar, and the diffusion sheet 4 realizes uniform light intensity over the entire front surface. The prism sheet 5 functions to control the light path so that light traveling in various directions through the diffusion sheet 4 is transformed within a range of viewing angles θ suitable for enabling the image to be viewed by an observer. Further, a reflection sheet 2 is provided under the light guide plate 5 to reflect light, which does not reach the liquid crystal panel 6 and is outside of the light path, so that such light is used again, thereby increasing the efficiency of use of the light source.
In this way, in order to effectively transfer such emitted light to the liquid crystal panel, a plurality of films having various functions is mounted, thereby causing light interference, including a Newton's Ring phenomenon, occurring as a result of use of the plurality of films, or a wet-out phenomenon, by which air is removed from the contact surface between the films. Further, while light is passed through the plurality of films, light is considerably lost due to scattering or absorption, and furthermore, the films may be damaged, attributable to physical contact between the films, undesirably entailing problems of low productivity and increased costs.
In the conventional prism film, in addition to a substrate layer and a prism layer constituting the prism film, there has been illustrated the case in which the other surface of the substrate layer is provided with diffusion particles. However, this case is disadvantageous because limitations are imposed on the effective diffusion of light, and light through the interface of the diffusion particles must pass through the substrate layer before reaching the prism layer, and thus, the loss of light still occurs.